What does magnetic resonance imaging add to the prenatal sonographic diagnosis of ventriculomegaly?

Abstract

Objective: The purpose of this study was to determine the contribution of magnetic resonance imaging (MRI) in evaluating fetuses with the sonographic diagnosis of ventriculomegaly (VM).

Methods: Over 4 years, consecutive fetuses with the sonographic diagnosis of VM at 1 facility who underwent prenatal MRI at a second facility were included. The roles of MRI and follow-up sonography were tabulated. The patients were analyzed in 2 groups based on the presence or absence of other central nervous system (CNS) abnormalities.

Results: Twenty-six fetuses with a gestational age range of 17 to 37 weeks had sonographically detected VM (atria > or =10-29 mm), including 19 with mild VM (atria 10-12 mm). In group 1, 14 had isolated VM, 6 of which reverted to normal by the third trimester. Magnetic resonance imaging showed cerebellar hypoplasia not shown by sonography in 1 fetus and an additional finding of a mega cisterna magna in a second fetus. In group 2, 12 fetuses had VM and other CNS anomalies on sonography. Additional findings were seen with MRI in 10 of these fetuses, including migrational abnormalities (n = 4), porencephaly (n = 4), and 1 diagnosis each of abnormal myelination, hypoplasia of the corpus callosum, microcephaly, a kinked brain stem, cerebellar hypoplasia, and congenital infarction. There were significantly more fetuses with additional CNS anomalies found by MRI among those in group 2 compared with those in group 1 (Fisher exact test, P = .001).

Conclusions: Although sonography is an accurate diagnostic modality for the evaluation of fetuses with VM, MRI adds important additional information, particularly in fetuses in whom additional findings other than an enlarged ventricle are seen sonographically.

Figure 1

Fetus at 37 weeks with large germinal matrix cysts. A and B, Axial (A) and sagittal (B) sonograms show enlarged ventricles with cysts (arrow) impinging on the frontal horns. C and D, Axial MR images show the cysts with the cyst walls (arrowheads) shown impinging on the frontal horns. In addition, there is a diffuse abnormal signal in the white matter, suggesting abnormal myelination.

Figure 2

Fetus at 23 weeks with borderline VM and a question of heterotopia. A and B, Axial sonograms show nodular irregularities (arrows) of the ventricular lining. C and D, Axial MR images show nodular elongated areas with a dark signal (arrows) lining the ventricles. This may represent early areas of heterotopia. Other findings (not shown) were a 2-vessel cord and an echogenic bowel. The fetus died in utero within 1 week after the imaging.

Figure 3

Fetus at 22 weeks with ACC. A and B, Axial sonograms show borderline VM (calipers) with a parallel orientation of the frontal horns (arrows), consistent with ACC. C, Axial MR image shows an appearance similar to that of the ventricles (arrows). D, Sagittal MR image shows an irregular contour of the ventricle and occipital cortex (arrow), suggesting an early appearance of a migrational abnormality that was not visualized sonographically.